The AO system for the GTC -an update Nicholas Devaney, Dolores Bello, Bruno Femenía, Alejandro Villegas, Javier Castro Grantecan, Instituto de Astrofísica de Canarias Marcos Reyes, Jesús Jimenez Instituto de Astrofísica de Canarias

Summary XSpecifications XStatus of Design XInterface with AO Instrument XThe PDR XPlanning

Preaching to the converted....(I hope!) Log scaling to show PSF structure due to segmentation. Integration will smooth this structure to ~Airy rings as pupil rotates

GTC AO specifications XCorrection in the near IR  m (goal:  m) XOn-axis Strehl ratio > 0.75 at 2.2  m when r 0 =20cm at 0.5  m (bright guide star) XSR > 0.1 a 2.2  m for guide star m R >14.5 XCorrected field = 1 arcminute (goal 2 arcmin) XRange of zenith angles 0-60  XTransmission to science focus > 70% (1.0 < < 2.5  m) XEmissivity < 20% a =3.8  m

Seeing stats at GTC site

Bright star Strehl ratio

AO system outline XWhole system mounted on a fixed bench at Nasmyth. Optical derotation of image. XDeformable mirror has 21 actuators across the pupil (11.309m=pupil+3% radius) actuators in use XTip-tilt correction carried out by GTC M2 4residual corrected by deformable mirror XShack-Hartmann wavefront sensor 4tip-tilt derived from Shack-Hartmann measure 4Designed to upgrade for use with Sodium Laser Guide Star

AO system outline

GTCAO optical design XCorrector: 4optical de-rotator 42 off-axis parabolas 42 DMs conjugate to atmospheric layers at 0 and 8 km altitude 4Beamsplitter 4ADC in the science path XWavefront Sensor 4field lens (maintains pupil distance) 4collimator 4camera 4ADC included

Optics design - Correction system deformable mirror (pupil) fold mirror (8km) OAP1 OAP2 ADC dichroic

Optical design of WFS Field lens ADC Lenslet array camera collimator

Mechanical design Scientific Instrument AO system

Wavefront sensor

Faint guide star performance J H k CCD60 CCD50 Proabability of finding star in  =1.5 arcmin at NGP is 13% for mR=15.0, 29% for mR=16.5

Interface with AO Instrument XOutput beam focal ratio same as GTC XDichroic cut-off at 0.9  m XDistance of exit pupil from focus = 6680mm (goal was to leave at position GTC exit pupil) XNeed to fix tolerance on output beam position and direction 4affects tolerances of AO alignment 4current values  6’’,  3mm XNon-common path errors will be measured using Phase Diversity; may affect focus range of AO Instrument (or detector). Will probably be measured by moving the wavefront sensor

Interface with AO Instrument 2400mm 600mm

Mechanical design Scientific Instrument Optics bench AO system Image rotator

Comments on comments.... XKeep loop closed while nodding 4main problem is repeatability: 4Jitter of arcsec corresponds to SR=0.96 at 2.2  m. In the image plane, this is 3.3 microns !!!! XIR WFS 4good in regions of high obscuration 4otherwise less sensitive (higher read noise and background) 4best to have both IR and vis.

Upgrade path... XThe first upgrade should be install a sodium laser guide star for single-conjugate operation 4This will provide good sky-coverage and allow more science XDevelopment of suitable sold state lasers is on- going (LLNL, CTI, Lightwaves, ESO...). Considering to contribute to development costs now. XThere should be a parallel development of MCAO wavefront sensing.

The PDR XDates fixed July XThree external reviewers confirmed XMechanical design not as advanced as would be expected for PDR. Control system not designed. XList of documents for PDR:

PDR Documents

AO Common user Science Instrument XFRIDA collaboration just started 4Main contributors: 4Optics: Mexico and U. of Florida 4Mechanics: Mexico and IAC 4Software and detector control: IAC XPreparing a conceptual design. Should be ready by October 2004 XInitial discussions are focussing on an imager and IFU spectrograph 4Resolutions foreseen range from 500 to about XPeople willing to contribute should contact Beto López

Planning